1. Field of the invention
The present invention relates to a semiconductor laser device and method of manufacturing the same, and particularly to a semiconductor laser device of high reliability and high output power obtained by improving a process of etching a semiconductor layer made of nitride semiconductor, and method of manufacturing the same, Specific composition of the nitride semiconductor element may be, for example, GaN, AlN, InN, AlGaN that is a mixture of the former, InGaN, AlInGaN and other semiconductors based on nitride of III-V group elements.
2. Description of the Related Art
Nitride semiconductor is capable of emitting light in a wide spectrum from ultraviolet region of relatively short wavelength to visible region including red, and is widely used as the material to manufacture semiconductor laser diodes (LD) and light emitting diodes (LED). Semiconductor laser devices made of nitride semiconductor, in particular, have been improved in compactness, long service life, reliability and output power, so as to be used as the light source for personal computers, electronic apparatuses such as DVD, medical equipment, industrial process machinery and optical communications.
The semiconductor laser device made of nitride semiconductor has such a constitution as an n-type contact layer, a crack preventive layer, n-type cladding layer, an n-type optical guide layer, an active layer, a p-type electron confinement layer, a p-type optical guide layer, a p-type cladding layer, a p-type contact layer and the like stacked one on another on a substrate usually made of sapphire (stacked structure). A stripe-shaped waveguide region is formed by forming a stripe-shaped ridge by etching or forming a current pinching layer. Resonator surfaces are formed on both sides of the waveguide region. Laser beam can be emitted by reflecting the light emitted in the active layer and causing resonation thereof (refer to, for example, to Japanese Unexamined Patent Publication (Kokai) No. 2001-332796). The portion that has the function to confine light and/or electrons in a striped configuration such as the ridge and current pinching layer and the resonator surface that contributes to stimulated emission have direct influence on the characteristics of the laser device. Therefore these portions require processing with extremely precise control.
In the process of manufacturing the semiconductor laser device, in addition to the processing of the stacked structure as described above, functional films such as electrodes and protective films are provided at predetermined positions. These functional films must be formed with the position and thickness being carefully controlled, so as to make the semiconductor laser of high output power with a satisfactory yield. An end face protective film formed on the end face from which laser beam emerges, in particular, must have high quality since the increasing output power imposes stricter demand on the end face. An end face protective film having uniform quality can be made, for example, by forming the protective film on the end face after processing the semiconductor layer in bar shape (laser bar), instead of forming the protective film before dividing the wafer.
In case the end face protective film is formed in the state of laser bar, however, if the component of the end face protective film spreads to the top surface and bottom surface of the laser bar when forming the film, the end face protective film (insulating film) is deposited also on metal layers such as electrode, resulting in an adverse effect on the operation of the device. For this reason, it is necessary to prevent the component of the end face protective film from spreading to the top surface and bottom surface of the laser bar so as to avoid the adverse effect on the operation of the device. The end face protective film may be prevented from spreading to undesirable portions by, for example, using a tray having a groove formed thereon and placing the laser bar in the groove. The laser bar is made to a length that corresponds to the length of a resonator, which is substantially constant. Therefore, it may be hoped that the end face protective film can be formed on the laser bar in satisfactorily controlled manner by forming the groove of a specified shape in advance. In order to provide a semiconductor laser device having excellent characteristics, it is important to carry out the processing of the stacked structure as well as the formation of the functional films on the stacked structure in satisfactorily controlled manner.